1. Field of the Invention
The invention relates to the use of an integrated container for lyophilization, storage, distribution, and processing of fluids, cells or tissues.
2. Description of Related Art
Distribution of materials requires storage under conditions suitable for optimum product stabilization, minimum storage cost, and simple operation at site of use. This is of particular importance in the field of biopharmaceuticals because of the propensity of such products to lose their biological activity in the liquid, aqueous state. Cooling below −20 degrees Celsius (° C.) is a popular approach, but costs of maintaining the materials at reduced temperatures (−20°, −80° or −196° (C.)) for extended periods and during transport are high. Additionally, many important biological products, such as blood and plasma, have high mass (weight), which in turn creates the shipping challenges of logistics and expense.
A typical example of a biological material susceptible to the above challenges is blood plasma. With whole blood having a limited storage life, blood plasma and its ability to keep for two years (either frozen or lyophilized) has long been an important medical product, particularly in hospitals and military operations. Transporting blood plasma per se is problematic due to the need for temperature controls and due to the high mass of its primary constituent, water. Even when blood plasma is lyophilized to remove the water and its attendant disadvantages, storage, transport and processing for use become no easier because the container is fixed prior to lyophilization and because of the documentation and rehydration requirements of such products.
Lyophilization is a useful mode of storing many biological products, and involves the processes of freezing, removal of water as vapor (under a vacuum), storage, and rehydration prior to use. Existing methods for lyophilizing aqueous biological materials depend upon the use of a rigid container, which can withstand the vacuum imposed within the container to sublimate the water for removal as water vapor. The water vapor is removed via a connection to the neck of the container, with storage and shipment resulting in large amounts of wasted space, namely, the space formerly occupied by the water. If further processing is required after hydration with pyrogen-free water, such as removal of certain constituents by filtration or dialysis, the product must be transferred to a new container. Aseptic conditions are essential, but many manipulative steps can compromise sterility.
Some examples of materials that undergo such processing include: vaccines; extracts from animal, vegetable, bacterial, yeast sources; proteins and carbohydrates sensitive to heat; oligonucleotides; organometallics; liposomes; antibiotics; and blood products. In such applications, during the manufacturing process, the products are lyophilized for later rehydration as needed. Additional applications in genetic engineering, biochemistry, biotechnology, cell biology, and medicine include storage of bacterial, mammalian, yeast, and plant cells. In such situations, a “cryostabilizing” agent, such as mannitol or trehalose, is added to the cell suspension before freezing. After storage and rehydration, these agents should be removed before the cells can be used for direct therapeutic application.
Cost-effective lyophilization requires a confined container that does not hinder the processing of the biological material. At a minimum, such processing requires: a simple means of applying a vacuum to the frozen solution; the use of a container with mechanically strong walls to withstand the pressures created during the vacuum; provision of a maximum surface to volume ratio for the frozen materials in order to facilitate egress of water vapor from the frozen matrix; and simple removal of the product when needed. Both rigid bottles and pliable bags for storage of fluids and cells are widely used, often featuring compartments separated by a common wall. Common wall materials available for such units range in their water vapor permeability from zero to high permeability.
One common lyophilization approach involves “shell freezing” materials within wide mouth glass flasks that are attached to a vacuum system. The water vapor exits from the mouth by sublimation and when completed, the vacuum is released and the flask is sealed and removed for storage. The disadvantages of this approach include the large size of the container to be stored, the fragility of the glass container, and the difficulty of maintaining aseptic conditions during the process.
W.L. Gore & Associates recently introduced a system that addresses many of these disadvantages (Genetic Engineering News 22: pp. 22 and 26, Jan. 1, 2002). Their approach involves the use of a disposable lightweight tray composed of a filling port on one of five rigid walls with a permeable Gore-Tex® expanded polyytetrafluoroethylene (ePTEE) laminate developed for this process. The laminate material has a microporous “body” to which a large mesh cover is attached for structural stability. The material was designed to provide a high vapor transfer rate and integrity to prevent passage of microorganisms, such as Bacillus subtillis and Bacillus licheniformis. The process involves filling of the container with the material to be lyophilized by freezing, placing the tray into a vacuum chamber, transferring of the water through the ePTEE membrane, returning the container to atmospheric conditions, and removing of the tray from the vacuum chamber for storage.
Despite the advances accorded by this approach, several critical features either have not been addressed or have been specifically excluded. First, containers are not provided in a sterile condition but contain specific instructions that any such sterilization is the sole responsibility of the user. Steam sterilization can be used, if necessary, but other useful procedures are either not recommended (e.g., radiation techniques) or are not addressed (e.g., ethylene oxide, gas plasma, formaldehyde gas, hydrogen peroxide vapor). Second, after removal of the water, the container is returned to the atmosphere, and the product cannot be stored under a vacuum due to the “open” nature of the ePTEE materials. This allows interaction of the lyophilized materials with oxygen and atmospheric water vapor during storage. Third, the ePTEE surface must be sealed with a foil barrier pouch or other vapor barrier enclosure to prevent product rehydration. This requires additional post-processing steps. Fourth, the rigid nature of the tray system precludes the integration and use of such a system into processes that involve centrifugation and decantation of fluids and cell suspensions (e.g., blood cell fractionation). Finally, the approach does not allow for facile exchange of the solution after lyophilization (e.g., removal of mannitol). This precludes the use of a single package for the storage and delivery of cells by infusion.
Accordingly, a need remains for a lyophilization method and apparatus that overcomes the prior art problems of wasted storage space, potential compromise of sterility, and multiple method steps in more than one container.